There have been times when I have felt my ignorance about Waterloo to be immense, capable itself of covering an area the size of the battlefield. Under these conditions, the temptation is simply to tiptoe away from the subject, consoling yourself with the thought that at least you know the names of the opposing generals, the country Waterloo is in, and that it happened 200 years ago exactly. Oh, and who won.

Which is why the idea behind this short book is so superbly useful. It places to one side the huge, cinematic panorama of history and instead concentrates on one particular farmhouse, on one particular day: 18 June 1815. History is vivified, lifts itself off the page and into the mind, when an expert zooms in on the details – and here the details are compelling. For the course of one day, 400 soldiers, wet, cold, in some cases hungover, who had bivouacked for the night in an abandoned farmhouse at La Haye Sainte, near a crucially strategic crossroads, found themselves staring down the massed barrels of Napoleon’s vanguard – and held them off. Had they not done so, Napoleon would have been able to get at Wellington’s troops before his Prussian reinforcements arrived, and in all likelihood Waterloo would have been a French victory instead; it would now be the name of a train station in Paris rather than London. All sorts of other things would have been overwhelmingly, unrecognisably different, too. Indeed, the circumstances of this one, relatively small, battle were so unlikely that it makes one think of counterfactual history, but with this twist: that we are, ourselves, now living in a counterfactual timeline, one in which some bored historian had posed the question: what if Major Baring and his 400 men had held off Napoleon’s thousands at the La Haye Sainte farmhouse?

The brevity of this remarkable book belies the amount of work that went into it. One can only marvel at how well Professor Simms has gone through the original sources – the surviving journals, reminiscences and letters of the individual combatants – to produce a coherent and gripping narrative. A battle may seem, from a distance, whether a physical or temporal one, to be a matter of abstraction: like a game of chess, or Risk, the mass movement of “forces” rather than the bloody, horrific work of hand-to-hand fighting by desperate men (and boys: there were 14-year-olds in these armies).

But here we have great events determined by the individual bravery and resource of soldiers in a homely place: the pigsty, the orchard, the kitchen garden. There are soldiers shoving their rifle barrels through knotholes in wooden fencing and having them grabbed by soldiers on the other side. Riflemen who have been shot in the head soak a cloth in rum, tie it round the wound and then carry on. Officers check the fallen to see that none of them is feigning death. There are commanders and enlisted men who refuse to leave their posts, or each other’s side. Soldiers hide under beds, for goodness’ sake. (This would have been my own preferred course of action.) The whole terrifying and chaotic nature of battle is made very clear, right down to listening, during the night, to the groans of the wounded and dying; feeling the dryness and grit in the mouth caused by tearing open packets of gunpowder with your teeth.

The aforementioned Major Baring emerges as the great hero of the day. In command of a multinational band, mainly Germans of the King’s German Legion (it is salutary to be reminded of a time when we fought alongside Germans, and not against them), he managed to combine courage and resourcefulness with shrewd strategic sense to the point where he and his men, despite taking staggering losses, were able to fight to the last bullet. “Baring’s example,” writes Simms in his afterword, “is therefore the very opposite of the Thermopylae or ‘Stalingrad’ complex in German military history, where soldiers sacrifice themselves in total, whether usefully or pointlessly.” And another thing I learned about Waterloo: that it was, in the words of a former British chief of defence staff, “the first Nato operation”.